1. Field of the Invention
The present invention relates to electrical switches and, more particularly, to electrical switches of the type having a contact receiving cavity that is hermetically sealed.
2. Brief Description of the Prior Art
It is found to be desireable to completely seal off the contacts of small switches such as subminiature switches from atmosphere contaminants such as moisture and dust. This is necessary because contaminants can enter the switch housing from around the switch terminals, through openings in the switch housing or from any of the interfaces of the various switch housing components. This may occur during a wave soldering operation. Any contaminant which enters the contact blade assembly of a switch may cause the switch to fail due to corrosion and other modes of failure.
One type of switch where sealing is found to be successful is in keyboard switches. Examples of arrangements which provide effective sealing for keyboard switches are disclosed in the following Patents:
U.S. Pat. No. 3,657,492 issuing Apr. 18, 1972
U.S. Pat. No. 3,749,859 issuing July 31, 1973
U.S. Pat. No. 3,829,632 issuing Aug. 13, 1974
U.S. Pat. No. 3,978,297 issuing Aug. 31, 1976
U.S. Pat. No. 3,996,428 issuing Dec. 7, 1976
U.S. Pat. No. 4,018,999 issuing Apr. 19, 1977
As the above patents disclose, it is easy to effect a hermetic seal by providing a mylar or other type of plastic-type sheet in a substrate which comprises the switch assembly. The sealing is found to be relatively simple in that the entire switch assembly is basically flat. This means that all components of the assembly comprising the substrate are in parallel adjacent planes. It is, therefore, not difficult to provide an adhesive or heat sealing process to the sealing sheet to provide the required hermetic seal.
The problem is considerably different when dealing with a switch assembly having a base member with a contact receiving cavity which is open at the top and defined by a floor that is laterally closed by side wall means. Switch assemblies of this kind usually have a first terminal means in the cavity adapted for electrical connection to outside circuitry and a second terminal means in the cavity adapted for electrical connection to outside circuitry having a resilient contact blade portion with an end spaced from the first terminal means. The contact blade portion is moveable between a normally open position wherein the end is spaced from the first terminal means and a closed position wherein the end contacts the first terminal means. A cover is provided to be mounted over the base member and has means for mounting an actuator assembly thereon. An actuator assembly is mounted in association with the mounting means of the cover to turn the switch between its on and off states.
The main concern with the structure of the type defined is to prevent contaminants from entering the interface between the cover and the base member and/or the mounting means where the actuator assembly is mounted. Seal arrangements have been provided in switch assemblies of the type described to prevent contaminants from entering the area where the actuator assembly is mounted. Examples of this type of seal are disclosed in U.S. Pat. No. 3,558,423 issuing June 1, 1971 and U.S. Pat. No. 3,789,176 issuing Jan. 29, 1974. Even though these arrangements effectively seal the area where the actuator assembly is mounted, a secondary operation must be provided to seal the interface between the cover and the base member. For example, in U.S. Pat. No. 3,558,423 the mating surfaces between the cover and base member are sealed by means of an epoxy resin.
Another problem which is prevelant with subminiature switches is to provide an actuator assembly arrangement that can be easily assembled. It can be appreciated that extremely small components must be used which are not easily handled in any assembly-type operation.